Aircraft tire and runway interface friction map consolidation

ABSTRACT

In various embodiments, a method associating received coefficient of friction data to runway friction estimation map elements. Also, the method may include aggregating the received determined coefficient of friction data into a friction estimation map.

FIELD

The present disclosure relates to brake control systems, and moreparticularly, to a system for exploiting known runway frictioncharacteristics.

BACKGROUND

Aircraft landing gear and aircraft wheels are typically equipped withbrakes in order to stop an aircraft after landing or during a rejectedtake-off braking stop. Generally, a braked wheel can be described asexperiencing one of four conditions; unbraked (synchronous speed),braked but not skidding (slip velocity less than critical value),skidding (slip velocity greater than critical value), or fully locked.

Historically, prior to landing, having prior knowledge of various runwayconditions was not possible. Accordingly, without prior knowledge ofrunway conditions, brake control systems had to expend time to assessrunway conditions and enact operation during braking. This time toassess braking conditions and change performance resulted in a reductionin braking performance and the potential increase to stop distances.

SUMMARY

A method for receiving, by a central processor, coefficient of frictiondata and slip ratio of a first series of locations along a runway. Themethod may include associating the coefficient of friction data torunway friction estimation map elements. The method may includereceiving coefficient of friction data for a first series of locationsalong the runway from a first aircraft. The method may include receivingcoefficient of friction data for a second series of locations along therunway from a second aircraft. Also, the method may include aggregatingthe received determined coefficient of friction data for the firstseries of locations along the runway from the first aircraft and thedetermined coefficient of friction data for the second series oflocations along the runway from the second aircraft into a frictionestimation map.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the present disclosure is particularly pointed outand distinctly claimed in the concluding portion of the specification. Amore complete understanding of the present disclosure, however, may bestbe obtained by referring to the detailed description and claims whenconsidered in connection with the drawing figures, wherein like numeralsdenote like elements.

FIG. 1 illustrates, in accordance with various embodiments, a front viewof an aircraft on a runway;

FIG. 2 illustrates, in accordance with various embodiments, a top viewof an aircraft on a runway;

FIG. 3 illustrates, in accordance with various embodiments, a blockdiagram of a brake control unit;

FIG. 4 illustrates, in accordance with various embodiments, a simplifiedgraph depicting coefficient of friction vs. slip ratio curve;

FIG. 5 illustrates, in accordance with various embodiments, a method forexploiting on ground wheel braking for estimation of a coefficient offriction vs. slip ratio curve;

FIG. 6 illustrates, in accordance with various embodiments, an exampleof a friction element of a runway;

FIG. 7 illustrates, in accordance with various embodiments, a method formapping coefficient of friction vs. slip ratio curve data; and

FIG. 8 illustrates, in accordance with various embodiments, a centraldatabase/central friction map (CFM) computing device 800.

DETAILED DESCRIPTION

The detailed description of exemplary embodiments herein makes referenceto the accompanying drawings, which show exemplary embodiments by way ofillustration and their best mode. While these exemplary embodiments aredescribed in sufficient detail to enable those skilled in the art topractice the disclosure, it should be understood that other embodimentsmay be realized and that logical, chemical, and mechanical changes maybe made without departing from the spirit and scope of the disclosure.Thus, the detailed description herein is presented for purposes ofillustration only and not of limitation. For example, the steps recitedin any of the method or process descriptions may be executed in anyorder and are not necessarily limited to the order presented.Furthermore, any reference to singular includes plural embodiments, andany reference to more than one component or step may include a singularembodiment or step. Also, any reference to attached, fixed, connected orthe like may include permanent, removable, temporary, partial, fulland/or any other possible attachment option. Additionally, any referenceto without contact (or similar phrases) may also include reduced contactor minimal contact.

In general, a tire, wheel, brake rotors and axle rotate together. Theopposite of a skid event is the condition where the tire, wheel, etc.,rotate freely at a speed equivalent to the translational axle speed.This equivalent speed without any deceleration is referred to as thesynchronous wheel speed. As the brakes are applied, torque is generatedwhich slows the rotational speed of the wheel. This causes the wheel torotate at a speed slower than the synchronous speed. This differencebetween synchronous speed and equivalent braked speed represents theslip velocity. As the slip velocity or difference increases the tiredrag force created at the tire/runway interface increases, causing theaircraft to decelerate. This drag force increases until slip velocityreaches a value dependent on tire/runway conditions. As slip velocityincreases beyond this value drag force decreases. Thus, the goal ofefficient antiskid control is to maintain operation near this criticalslip velocity corresponding to the maximum drag force.

According to various embodiments, a map and/or a portion of a map may beproduced based on substantially real-time information regarding therunway characteristics for use during a landing event. This informationmay include slip ratio and coefficient of friction and/or the slip ratiopeak information according to position, such as according to variouspositions along runway 50 at various times, with brief reference toFIGS. 1 and 2).

According to various embodiments, a brake control system 101 (describedin greater detail in FIG. 5) may be configured to continuously assesstire/runway 50 friction properties, detect the onset of wheel skids, andcontrol brake torque to achieve efficient and smooth brakingperformance. Thus, brake control system 101 may utilize an algorithm,along with substantially real-time measured values to assist withcontrolling brake torque to achieve efficient and/or smooth brakingperformance. A history of wheel speed information, such as wheel speedinformation associated with one or more braking events (e.g., associatedwith a landing and/or braking stop), may also be used to iterativelyestimate tire/runway 50 friction properties.

Referring to FIG. 1, a front view of an aircraft 100 on runway 50 isillustrated according to various embodiments. Aircraft 100 may compriselanding gear including left main landing gear (“LMLG”) 110, nose landinggear (“NLG”) 120, and right main landing gear (“RMLG”) 130. Though at-gear type landing gear aircraft is depicted, it should be appreciatedthat the concepts described herein are applicable to aircraft havingmultiple axle pairs per gear and aircraft with more than two mainlanding gears. Each gear may comprise two wheels. For example, RMLG 130comprises right outboard wheel 132 and right inboard wheel 134. However,in various embodiments, aircraft 100 may comprise any number of gearsand each gear may comprise any number of wheels. Additionally theconcepts disclosed herein variously apply to two wheel aircraft (e.g.one wheel for each main landing gear).

Referring to FIG. 2, a top view of aircraft 100 on runway 50 isillustrated according to various embodiments. Thus, in variousembodiments, one or more aircraft 100 wheels may be in contact with thepavement of runway 50. Different coefficients of friction of runway 50at various positions, such as positions 52, 54, and 56, may cause thewheels of aircraft 100 to spin up at varying rates. In variousembodiments, the wheels associated with LMLG 110 may spin up faster thanthe wheels associated with RMLG 130 due to a higher coefficient offriction for runway 50 at one position versus another position. Invarious embodiments, runway 50 may comprise multiple contaminants, suchas ice, mud, oil, fuel, water and/or snow, each of which may affect ameasured/estimated coefficient of friction at various positions. Themeasured/estimated coefficient of friction at various positions alongrunway 50 may be time-specific. For instance, the measured/estimatedcoefficient of friction at various locations may change based onconditions over time.

Referring to FIG. 3, a system 300 for detecting on groundcharacteristics is illustrated according to various embodiments. System300 may comprise a brake control unit (BCU) 310. A brake control system101 may be a subsystem of brake control unit 310. Brake control system101 may be in communication with brake control unit 310. Brake controlsystem 101 may be communicatively coupled to left outboard wheel speedsensor 322, left inboard wheel speed sensor 324, right inboard wheelspeed sensor 326 and right outboard wheel speed sensor 328. Brakecontrol system 101 may comprise a left outboard tire pressure sensor332, left inboard tire pressure sensor 334, right inboard tire pressuresensor 336, and right outboard tire pressure sensor 338. Tire pressuremeasurements may be used to infer a weight and force present on thetires at various times/locations. The tire pressure measurement mayallow for an estimation of a tire spring constant. When coupled with atire radius information and position data, a force may be estimated ifnot directly measured. For instance, tire pressure coupled with the tireradius derived from the distance between an aircraft touchdown and wheelspeed sensor drop out positions allow for normal force estimation. Theelimination of the tire pressure measurement does not prevent thisestimation but may limit its fidelity.

A location sensor 330 may be coupled to brake control system 101 and/orbrake control unit 310. Location sensor 330 may be a GPS unit/receiver.Location sensor 330 may be configured to determine position of aircraft100 at each braked wheel location. Brake control unit 310 may be coupledto a transceiver 316. The various components may be electronicallycoupled. In various embodiments, the various components may communicatevia wireless and/or wired communications. For example, wheel speedsensors 322, 324, 326, 328 may transmit, via wired and/or wirelesstransmission, wheel speed measurements to brake control system 101 andin turn to brake control unit 310. The wheel speed sensors, pressuresensor and tire pressure sensors may be hard wired to BCU 310.Transceiver 316 may transmit the slip ratio vs. position data and thecoefficient of friction vs. position data to a central database/processing computer. This central data base/processing computer maybe a collection of each air plane's friction map for processing and/oraggregating,

Brake control unit 310 and/or brake control system 101 may comprise acomputing device (e.g., processor 312) and an associated memory 314.Memory 314 may comprise an article of manufacture including a tangible,non-transitory computer-readable storage medium having instructionsstored thereon that, in response to execution by a computing device(e.g., processor 312), cause the computing device to perform variousmethods.

Wheel speed sensors 322, 324, 326, 328 may measure a wheel speed. Wheelspeed sensors 322, 324, 326, 328 may comprise any device capable ofmeasuring a wheel speed. For example, in various embodiments, wheelspeed sensors 322, 324, 326, 328 may comprise electromagnetictransducers and/or fiber optic transducers. In various embodiments, thewheel speed sensors may comprise an AC sensor which uses a magnetsurrounded by a pickup coil in an axle of the landing gear. In variousembodiments, wheel speed sensors 322, 324, 326, 328 may comprise a DCsensor which may comprise a permanent magnet direct current generator,which outputs a voltage proportional to a rotational speed of itsarmature. Additionally, wheel speed sensors 322, 324, 326, 328 maydetect a change in a rate of deceleration of the wheels. The processingof wheel speed to produce acceleration is primarily performed by a brakecontrol algorithm (BCA) contained within the brake control unit 310. TheBCA processes the wheel speed, wheel acceleration, and brake pressure(hydraulic brake) or electric actuator (electric brakes) to calculatethe braking pressure/force best suited for the most desirable braking.This may reduce a skid to recover a more efficient braking or shortstopping distance. The resulting braking commands (e.g. pressure orforce) may tend to minimize skids and cause braking commands to achieveefficient brake operation and short aircraft stopping distance. Theresulting braking commands may correspond to gentle braking conditionsto achieve smooth braking.

The wheel speed may be the actual measured speed of the wheel. Invarious embodiments, each wheel on aircraft 100 may be equipped with awheel speed sensor 322, 324, 326, 328. However, in various embodiments,aircraft 100 may comprise a wheel speed sensor on any braked wheel.Wheel speed sensors 322, 324, 326, 328 may transmit (such as via a wiredcoupling) the wheel speed data to brake control unit 310. Brake controlunit 310 may calculate a reference wheel speed for each wheel. Thereference wheel speed may be the over ground speed that the wheel wouldbe travelling if the wheel were rolling without slipping. For example,if wheel speed sensor 322, 324, 326, 328 measures a wheel speed of 10radians per second for a wheel with a radius of 1 meter, brake controlunit 310 may calculate a reference wheel speed of 10 meters per second.During spin up and subsequent braking, wheels may be at least partiallyslipping. Thus, the wheel reference speed may be different from theactual speed of aircraft 100 during spin up and braking events. The BCAmay process wheel speed measurements which results in a wheel referencespeed. The wheel reference speed may be set equal to the wheel speedduring initial portions of a landing stop. The BCA wheel referencecalculations are designed to estimate the aircraft speed rejecting thewheel speed effects of skidding, spin ups, and/or the like. A skiddingor slipping wheel (after the key slip velocity threshold) produces lessdrag force. Thus, the aircraft is decelerated less but the wheelreference reflects the aircraft speed, not the wheel speed. Wheelreference speeds are estimations of aircraft speed and separate morefrom the wheel speed as a skid grows deeper.

Processor 312 may map the measured wheel speed measurements to aircraft100 position data on runway 50 to determine an estimate of thecoefficient of friction for portions of runway 50 and/or the slip ratioof the wheel. A skid may occur as the applied brake torque exceeds theavailable spin up torque created from the tire/runway interfacefriction. Processor 312 may utilize a measured wheel speed, calculatedacceleration, wheel reference and tire normal force estimation mapped toaircraft 100 position data on the runway 50 to determine an estimate ofthe coefficient of friction and/or the slip ratio as a function ofposition. In response to braking stops that involve the anti-skidfunction, peak wheel accelerations may be used to estimate a peakcoefficient of friction (see FIG. 4). The wheel speed and wheelreference may be used to estimate slip ratio. The peak wheelacceleration and tire normal force may be used to estimate thecoefficient of friction. The slip ratio value corresponding to the peakcoefficient of friction may define the peak slip ratio. In response tobraking stops that do not involve the anti-skid function, measured wheelspeed, calculated acceleration, wheel reference, and tire normal forceestimation may be used to estimate a lower bound of the wheel slip valueand/or coefficient of friction.

In response to a slow speed threshold (such as wheel speed sensordropout (about 10 kts, about 18.52 Km/hr)) an estimate of aircraft 100weight is obtained and the instantaneous runway 50 friction property maybe calculated for each of the braked wheels as a function of aircraft100 position data (previously recorded, such as by location sensor 330).A slow speed threshold may involve the aircraft being free from forceswhich would alter the tire normal forces. Estimating the weight of theaircraft may involve determining a tire pressure of a tire of the firstbraked wheel and calculating the weight of the aircraft based on thedetermined change tire pressure from a known reference value. This iscoupled with the distance between the aircraft touchdown position andlow speed threshold condition position. The tire pressure sensor helpswith the identification of the spring constant to associate with thetire and the distance and assists the identification of the tire radius.Aircraft position may be ascertained more than once after or beforewheel speed sensor drop out to verify tire radius. This may assist withthe estimation the tire normal force which is used to calculate thefriction property data. This calculation may be done “after-the-fact” asan accurate aircraft 100 weight measurement cannot generally be obtainedduring the landing due to transient lift and aircraft pitching due tobraking. This may include but is not limited to the aircraft pitchingwhich may occur during antiskid cycling. For instance, at certainspeeds, lift from the wings may substantially affect a weightmeasurement. Thus, this after-the-fact calculation may be made inresponse to aircraft 100 traveling at a speed where there is no liftadversely affecting the calculation.

Runway 50 touchdown and/or a low speed threshold location data may beobtained from a position/location sensor 330, such as a GPSunit/receiver. The positioning data may be used in conjunction with ameasured number of wheel rotations for each wheel. The wheel rotationcount and the wheel radius may be used to estimate the absolute runway50 positions; which, in turn, have associated slip and friction values(which may be calculated/extrapolated from the measured wheel speed,calculated acceleration, wheel reference and tire normal forceestimation at those locations).

This information may be transmitted to a system external to aircraft 100and made available for additional aircraft landing on runway 50. Thefindings of the actual location, e.g. portions of runway 50 traveled byaircraft 100, during a landing event, at various intervals may beaggregated with measured results of other aircraft having brake controlsystem 101 to develop an expanded knowledge of runway 50 and itscharacteristics for a period of time. Brake control system 101 maycreate a moving average of the data to identify longer-term trends ofthe coefficient of friction and/or the slip ratio as a function ofposition. This expanded knowledge of runway 50 characteristics may becommunicated to additional components of aircraft 100 and/or otheraircraft in the vicinity or expected to be in the vicinity so thatappropriate action may be taken.

In operation, in response to a touchdown associated with a landing onrunway 50, wheel speed information is collected. Initially, each wheelis subject to a spin up condition, to bring the wheels up fromsubstantially stationary to a rolling speed which is the same asaircraft 100 during landing. During this period, a touchdown protectionphase is enacted so that no brakes are applied. In response to a wheelspeed spin up and/or touchdown, a wheel reference value measurement ismade. A wheel reference value may be an estimate of aircraft 100 speedmeasured at each wheel. The reference speed may be updated at anysuitable time. For instance the reference speed may be continuouslyupdated throughout the braking event and continues until low speedthreshold condition. Thus, aircraft 100 equivalent speed which is theinstantaneous wheel speed and wheel reference data may be initialquantities for brake control system 101. Initially these values shouldbe substantially equivalent. In response to applying a brake, a dragforce is generated. In turn, these values (e.g. the instantaneous wheelspeed and the wheel reference value) separate. The brake pressure fromsensors 342, 344, 346, 348 and/or the tire pressure from sensors 332,334, 336, 338 may be measured at this time. Based on the frictiongenerated, the rotation of each wheel relative to aircraft 100 speed isdecreased. An aircraft reference speed is calculated/estimated and iscalculated as a weighted combination of the individual wheel referencespeeds.

Referring to FIG. 4, a graph depicting a coefficient of friction and/orthe slip ratio according to various embodiments is presented. This dataplotted at various times and/or positions may yield informationregarding conditions of the runway and capacities of the braking systemassociated with those conditions. Varied runway conditions will affectthe data. For instance, dry runway conditions may be associated withpeak 410. Wet runway conditions may be associated with peak 420. Icyrunway conditions may be associated with peak 430.

In response to measured brake pressure or brake actuator force, torquegenerated may be estimated. Brake pressure may be either increasing ordecreasing. In response to the slip exceeding the key peak value theincreasing brake pressure will result in decreasing drag force. Ameasured acceleration maximum during a period where aircraft 100 isgenerating wheel slips corresponds to the peak slip ratio as related inthe coefficient of friction vs. slip relationship. Thus, in response tomaximum accelerations being measured, an estimate of the slip ratiocurve and the value of coefficient of friction associated with the slipratio may be gleaned.

In response to this reduction in speed, a peak of a new slip curve maybe crossed. Each peak, 410, 420, 430 may correspond to a peakacceleration. In association with a braking stop, constant cycling willcreate multiple estimated peaks for the coefficient of friction vs. slipratio curve, and the threshold may be crossed multiple times andestablish new peaks at various plotted locations.

The peak of the new slip curve may be a peak friction point given theslip ratio. In response to a braking stop where there is no skidding,(e.g. no anti-skid system event), a lower bound to a slip ratio, and/ora lower bound for the coefficient of friction may be established. Thislower bound may establish that the wheel is at least capable of thismuch friction without a skid event. This information may be exploited byaircraft 100. Additional details regarding brake mapping data aredisclosed in co-pending U.S. patent application Ser. No. 13/968,060,filed Sep. 6, 2013, and entitled “BRAKE CONTROL SYSTEM COMPRISINGTIRE/RUNWAY FRICTION PROPERTY ESTIMATION MAPPING” having commonownership as the present application, the contents of which are herebyincorporated by reference in their entirety for any purpose.

Referring to FIG. 5, a process 500 for detecting an on groundcharacteristic is illustrated according to various embodiments. Asaircraft 100 prepares for landing, brake control unit 310 may be inapproach mode and measure feedback data (Step 510). In response toaircraft 100 landing, the wheels rotations may be spun up to aircraft100 speed (Step 520). Aircraft position may be measured (Step 520).Brake control unit 310 may collect additional data in response to thelanding. On ground position of the aircraft and/or wheel speed may bemeasured (Step 530). This may be done at any time and/or at any intervalof time. On ground braking active data feedback may be processed forestimation (Step 540). A determination whether the axle pair has reacheda wheel speed sensor drop out may be made. (Step 550). If not, return tostep 540. (Step 545).

The low speed threshold (e.g., wheel speed sensor drop out speed) sensormay be associated with the aircraft position within the runway system(Step 560). Aircraft position may be measured (Step 560). The tirepressure measurements and aircraft position data may be used/processedto estimate tire normal force (Step 570). Data for creating a map oftire/runway slip ratio and coefficient of friction estimation may beprocessed (Step 580). The tire/runway friction properties may betransmitted and/or stored by the system (Step 590).

The reference wheel speed and the instantaneous wheel speed will beginto separate as the brakes are applied and friction is produced. Thesevalues may be compared by processor 312 utilizing one or more algorithmsto determine a slip ratio as a function of aircraft position (Step 560).Acceleration maximums of the wheels may be noted as part of this process500. A coefficient of friction may be determined/estimated as a functionof position. These measured/estimated coefficient of friction values maybe mapped to relevant portions of runway 50 (Step 580). Measured valuesand/or determinations may be stored to memory 314 and/or transmitted bytransceiver 316. Note, the systems disclosed herein are applicable tobraking during landing and/or during a rejected take-off braking stop.

According to various embodiments, the data collected and determined bysystem 300 may be processed into a useful form or application. One ofthese forms is the creation of a runway friction estimation map. Thisrunway friction estimation map may be created by aggregating thedetermined estimated values captured by a plurality of aircraft landingevents. This aggregated, synthesized runway friction estimation map datamay be provided to an aircraft about to conduct braking or as braking isapplied during a stop. This may reduce calculation time and result inquicker and more efficient braking.

According to various embodiments, and with reference to FIG. 6, a runway50 or taxiway may be divided into friction elements from end to end andside to side. A central runway friction estimation map may be acollection of adjacent friction elements which substantially completelycover the utilized portions of a runway or taxiway. As depicted in FIG.6, a wheel, such as braked right outboard wheel 132, may travel downrunway 50. Each friction element is a generally rectangular region basedon the aircraft participating in the generation and use of the centralfriction estimation map. Generally, an individual friction element is arectangle whose width, W, is substantially equal to the correspondingaircraft tire's contact patch, W′. The length, L, of each individualfriction element may be substantially equal to the product of the periodcorresponding to the fastest antiskid cycling frequency (for exampleconditions associated with dry runway and maximum take-off weightconditions) and equivalent translational wheel speed or axel speed. Themost accurate friction property estimation occurs once per complete skidcycle under antiskid control operation. The friction property estimationmay then be assigned to the entire region contained within a singlefriction element.

Portions of the central synthesized friction estimation map may be basedon the smallest friction element in the collected individual aircraftfriction estimation map. The different friction elements associated withdifferent aircraft are aggregated together and mapped onto a collectionof base friction elements (corresponding to the smallest frictionelement) using simple relationships assuming data taken during thesimilar time frames. For example, mapping from larger friction elementsto smaller friction elements can simply equate the friction propertiesfor each smaller element whose geometric center lies within the largerfriction element. Also, to map smaller friction element frictionproperties to larger friction element may involve mapping the weightedaverage of all smaller friction element's properties to the largerfriction element if the smaller friction element's geometric center iscontained within the larger friction element rectangle.

For instance, in response to an aircraft 100 performing a braking stop(ex. landing stop or rejected take-off stop) the brake control unitassociated with the BCA (as described above) may create a portion of thedata to be utilized in a friction estimation map. This data to beutilized in a friction estimation map may be transmitted from theaircraft 100 to the central database/friction map algorithm forprocessing.

With brief reference to FIG. 8, the central database/central frictionmap (CFM) processor may comprise a computing device 800 (e.g., processor810) and an associated memory 805. The memory 805 may comprise anarticle of manufacture including a tangible, non-transitorycomputer-readable storage medium having instructions stored thereonthat, in response to execution by a computing device 800 (e.g.,processor 810), cause the computing device 800 to perform variousmethods. The computing device 800 may be coupled to a transmitter 825,receiver 820, transceiver, and/or network for sending and receivingdata. The computing device 800 may be coupled to a display 815configured to distribute data to a user.

The CFM processor may receive environmental data (ex. temperature,barometric pressure). The information of the CFM processor may undergotemporal weighting such that of successive friction estimation maps fromaircraft braking stops may properly combined into a singlerepresentative friction estimation map for a runway 50. The CFMprocessor initially transfers the specific aircraft 100 frictionproperty map data (friction properties and position data) onto a basefriction elements template. After mapping this friction property vs.position data onto the friction elements, e.g. locations where thewheels traversed the runway 50, the CFM processor may perform spatial(ex. distance weighted) processing in order to fill-in and/or estimatethe remainder of the friction elements.

The friction elements may be sized and located according to the aircraftproducing the data. The friction elements may be mapped to the basefriction elements (smallest sized friction elements in the collection offriction estimation maps). A time weighting method may be used tocombine the collection of friction estimation maps created over timeinto a single representative friction estimation map. This process maybe accomplished sequentially, such as a single friction element at atime, until all friction elements have been processed. For example, suchfiltering of friction element friction data will tend to de-emphasizeolder data in favor or more recent friction data. This temporalprocessing may be further enhanced through the influence ofenvironmental weighting (e.g., significant changes in air temperaturewithin the collection of friction estimation maps indicate differentweighting for different friction estimation maps). Friction data havingsimilar environmental metrics may be weighted more similarly than datawith different metrics. The single representative friction estimationmap having an average of data for appropriate regions (ex. brakeapplication region immediately after touchdown, brake applicationregions appropriate for RTO stops) and/or position specific data may beavailable for transmission to other aircraft which can exploit thisinformation.

The type of access to the CFM processor and the data acquired based onthat access (average and specific position) may affect how the data isutilized. For instance, in traditional landing schema, aircraftperforming braking without the benefit of friction estimation mappinginteract with the runway 50 and assess performance metrics within thebrake control algorithm (BCA) to converge to desired performance levels.Utilizing an average or representative information corresponding to theregions where the brakes will be initially applied affords theaircraft's 100 BCA the opportunity to use representative data to betterinitialize BCA controllers for the initial brake application region. Forinstance, an integrator or state of the BCA may be pre-set to a frictionlevel that is closer to an observed or empirically derived frictionlevel than having no known friction level. Utilizing friction propertydata corresponding to specific location and potentially throughout theentire braking stop (not just initial conditions) offers the aircraft'sBCA the advantage of greater accumulated runway 50 knowledge.

With reference to FIG. 7, a method 700 for building a runway frictionestimation map is disclosed. A determination that the aircraft hasperformed a braking stop on the runway or taxiway is made (step 705).Consistent with the prior disclosed methods, tire/runway frictionestimation map data is received from the aircraft 100 in concert with abraking stop process, such as a braking stop being completed (step 710).The tire/runway friction estimation map data may be populated torunway/taxiway friction elements (Step 715). The CFM processor mayreceive environmental data to perform a runway 50 friction elementupdate. The environmental data may be gathered from any source such as aweather providing system or on site sensors (step 720). Spatial and/ortemporal weighted calculations may be performed to compute updates tofriction elements (step 725). For instance, the system may determinerelative wheel locations based on aircraft 100 position data. Also, theCFM processor may estimate unknown friction element data from knownfriction element data. For instance, a known friction element proximateto an unknown friction element may be utilized to estimate the unknownfriction element. An average of known friction elements may be made toestimate an unknown friction element located between known frictionelements. Older in time determinations of friction elements may be givenless weight as compared to new friction element data. In this way,outdated data, such as due to changes in conditions due to weather, maybe accounted. The CFM processor may process the updated runway/taxiwayrepresentative friction element values for the entire runway/taxiway 50(step 730).

The CFM processor may compute updated runway 50 representative frictionelement values for the runway's 50 landing zone (step 735). The CFMprocessor may compute updated runway 50 representative friction elementvalues for the runway's 50 RTO braking zone (step 740). A determinationmay be made if an aircraft 100 requested general runway frictionestimation map data (step 745). In response to an aircraft 100 making ageneral runway 50 friction estimation map data request, representativefriction estimation map data may be transmitted to the aircraft 100prior to braking (step 750). General tire/runway friction data maycomprise an average value for a particular zone. A determination may bemade that the aircraft 100 has requested specific runway tire/runwayfriction data (step 755). Specific tire/runway friction data maycomprise substantially real-time based on a current position of a wheel.In response to the aircraft 100 making a specific runway 50 frictionestimation map data request, representative friction estimation map datamay be transmitted to the aircraft prior to braking (step 760).

Benefits, other advantages, and solutions to problems have beendescribed herein with regard to specific embodiments. Furthermore, theconnecting lines shown in the various figures contained herein areintended to represent exemplary functional relationships and/or physicalcouplings between the various elements. It should be noted that manyalternative or additional functional relationships or physicalconnections may be present in a practical system. However, the benefits,advantages, solutions to problems, and any elements that may cause anybenefit, advantage, or solution to occur or become more pronounced arenot to be construed as critical, required, or essential features orelements of the inventions. The scope of the inventions is accordinglyto be limited by nothing other than the appended claims, in whichreference to an element in the singular is not intended to mean “one andonly one” unless explicitly so stated, but rather “one or more.”Moreover, where a phrase similar to “at least one of A, B, or C” is usedin the claims, it is intended that the phrase be interpreted to meanthat A alone may be present in an embodiment, B alone may be present inan embodiment, C alone may be present in an embodiment, or that anycombination of the elements A, B and C may be present in a singleembodiment; for example, A and B, A and C, B and C, or A and B and C.Different cross-hatching is used throughout the figures to denotedifferent parts but not necessarily to denote the same or differentmaterials.

Systems, methods and apparatus are provided herein. In the detaileddescription herein, references to “various embodiments”, “oneembodiment”, “an embodiment”, “an example embodiment”, etc., indicatethat the embodiment described may include a particular feature,structure, or characteristic, but every embodiment may not necessarilyinclude the particular feature, structure, or characteristic. Moreover,such phrases are not necessarily referring to the same embodiment.Further, when a particular feature, structure, or characteristic isdescribed in connection with an embodiment, it is submitted that it iswithin the knowledge of one skilled in the art to affect such feature,structure, or characteristic in connection with other embodimentswhether or not explicitly described. After reading the description, itwill be apparent to one skilled in the relevant art(s) how to implementthe disclosure in alternative embodiments.

The term “coefficient of friction” as used herein may refer to the ratioof the force that maintains contact between an object and a surface andthe frictional force that resists the motion of the object. Thefrictional force may be equal to the coefficient of friction multipliedby the normal force on the surface. Slip ratio as used here may refer toa means of calculating and expressing the locking status of a wheel.Slip Ratio %=[(Vehicle Speed−Wheel Speed)/Vehicle Speed]×100.

One skilled in the art will appreciate that the systems and methodsdisclosed herein may employ any number of databases in any number ofconfigurations. Further, any databases discussed herein may be any typeof database, such as relational, hierarchical, graphical,object-oriented, and/or other database configurations.

Furthermore, no element, component, or method step in the presentdisclosure is intended to be dedicated to the public regardless ofwhether the element, component, or method step is explicitly recited inthe claims. No claim element herein is to be construed under theprovisions of 35 U.S.C. 112(f), unless the element is expressly recitedusing the phrase “means for.” As used herein, the terms “comprises”,“comprising”, or any other variation thereof, are intended to cover anon-exclusive inclusion, such that a process, method, article, orapparatus that comprises a list of elements does not include only thoseelements but may include other elements not expressly listed or inherentto such process, method, article, or apparatus.

What is claimed is:
 1. A method comprising: receiving, by a computingdevice comprising a central processor and a tangible, non-transitorymemory, coefficient of friction data of the first series of locationsalong the runway from a first aircraft; receiving, by the centralprocessor, coefficient of friction data for a second series of locationsalong the runway from a second aircraft; associating, by the centralprocessor, the coefficient of friction data to runway frictionestimation map elements; and aggregating, by the central processor, thereceived determined coefficient of friction data for the first series oflocations along the runway from the first aircraft and the determinedcoefficient of friction data for the second series of locations alongthe runway from the second aircraft into a friction estimation map forthe runway.
 2. The method of claim 1, further comprising performing, bythe central processor, spatial calculations to form the frictionestimation map.
 3. The method of claim 2, wherein the spatialcalculations comprise extrapolating a wheel position from a firstaircraft position based on at least one of an aircraft type and ageometric setup of landing gear of the first aircraft.
 4. The method ofclaim 2, wherein the spatial calculations comprise estimating unknownrunway friction estimation map elements based on nearest neighbor knownrunway friction estimation map elements.
 5. The method of claim 1,further comprising performing, by the central processor, temporalcalculations to form the friction estimation map, wherein the temporalcalculations comprise weighting current data heavier than less currentdata for overlapping runway friction estimation map elements.
 6. Themethod of claim 5, wherein the length of an individual friction elementis substantially equal to the product of a period corresponding to thefastest antiskid cycling frequency and equivalent translational wheelspeed and the width of an individual friction element is substantiallyequal to the width of an aircraft wheel.
 7. The method of claim 1,further comprising receiving, by the central processor, environmentaldata related to the runway.
 8. The method of claim 1, further comprisingtransmitting, by the central processor, the friction estimation map forthe runway to a third aircraft for exploitation.
 9. The method of claim1, further comprising associating a time stamp with at least one of thereceived coefficient of friction data for the first series of locationsalong the runway from the first aircraft and the received coefficient offriction data for the second series of locations along the runway fromthe second aircraft.
 10. A system comprising: a tangible, non-transitorymemory communicating with a central processor configured to aggregatecoefficient of friction data, the tangible, non-transitory memory havinginstructions stored thereon that, in response to execution by thecentral processor, cause the central processor to perform operationscomprising: receiving, by the central processor, determined coefficientof friction data for a first series of locations along a runway from afirst aircraft of a plurality of aircraft; associating, by the centralprocessor, the coefficient of friction data to runway frictionestimation map elements; receiving, by the central processor, determinedcoefficient of friction data for a second series of locations along therunway from a second aircraft of the plurality of aircraft; andaggregating, by the central processor, the received determinedcoefficient of friction data for the first series of locations along therunway from the first aircraft and the coefficient of friction data forthe second series of locations along the runway from the second aircraftinto a friction estimation map for the runway.
 11. The system of claim10, further comprising performing, by the central processor, spatialcalculations to form the friction estimation map.
 12. The system ofclaim 11, wherein the spatial calculations comprise extrapolating awheel position from a first aircraft position based on at least one ofan aircraft type and a geometric setup of landing gear of the firstaircraft.
 13. The system of claim 11, wherein the spatial calculationscomprise estimating unknown runway friction estimation map elementsbased on nearest neighbor known runway friction estimation map elements.14. The system of claim 10, further comprising performing, by thecentral processor, temporal calculations to form the friction estimationmap, wherein the temporal calculations comprise weighting current dataheavier than less current data for overlapping runway frictionestimation map elements.
 15. The system of claim 10, further comprisingreceiving, by the central processor, environmental data related to therunway.